This invention relates to combustion heaters for water, and more particularly to a booster utilizing an infrared burner for efficiently raising the temperature of water to a desired level for use by a downstream user, generally a commercial warewashing apparatus.
Commercial washing apparatuses, such as conveyor and door type model warewashing or dishwashing machines, generally require water at a temperature of between 120.degree. and 160.degree. F. during washing cycles. This water can generally be obtained cheaply and easily from the central hot water supply of most buildings. Furthermore, keeping the water at this temperature does not usually pose a problem since most warewashers are equipped with a supplemental heating source located in the wash water holding tank in order to keep the water within the desired temperature range for washing.
However, in order to comply with health regulations, warewashing systems that do not utilize a sodium hypochlorite sanitizing system or the like are required to sanitize the ware being washed with a rinse using a minimum of 180.degree. F. water. Furthermore, the use of a 180.degree. F. water rinse is desirable because it facilitates the drying of the ware, thereby decreasing the turnaround time necessary for reuse. This high temperature is generally out of the range available from most buildings central hot water source. Thus, in order to supply water at this desirable temperature, boosters have been employed to raise the temperature of the incoming water from between 110.degree. and 140.degree. F. to the required sanitizing temperature of 180.degree. minimum.
For a typical application, the required water supply rate for a given booster can vary from between 60 to 400 gallons per hour and the required temperature increase can vary from 30.degree. to as much as 80.degree. F., depending on the temperature of the water received from the primary water supply. During busy periods the demand for this water can be quite large, thereby requiring that the booster be capable of continuously supplying a minimum of 180.degree. water at the required final rinse flow rate. Additionally, in order to insure easy installation, equipment of this type is generally subject to certain dimensional restrictions. Typically, the booster will be required to fit under a counter height of approximately 34 inches and within a counter depth of between approximately 25 to 30 inches. Furthermore, a clearance of at least 6 inches is generally required underneath the equipment to facilitate the cleaning of the floor. Further adding to the design constraints for boosters of this type is the fact that they should be simple to operate and easy to maintain. Finally, in order to reduce operating costs, heat losses, other than to the water being heated, need to be kept to a minimum.
Electrically heated booster water heaters are available which generally meet the above requirements. These electric heaters have been attractive to consumers since their initial cost is relatively low and installation is relatively easy. However, heaters of this type are very expensive to operate. Other booster water heaters are known which utilize a blue-flame gas fired heater to supply hot water at the sanitizing temperature. There are many prior art patents for heaters of this type, including U.S. Pat. No. 3,160,145 which discloses a gas fired water heater having a blue flame gas burner at atmospheric pressure disposed below a horizontally mounted finned tube heat exchanger. Heaters of this type are not without problems, though. They are known to produce a noise known as "flame roar" while igniting which can be annoying and distracting to workers. Also, when used to supply sanitizing water at 180.degree., they are relatively inefficient since in many prior art designs more water is heated to the 180.degree. temperature than is necessary and the remainder is then mixed with cold water to supply primary hot water at 140.degree. to other sources.
Accordingly, boosters have been developed which use high efficiency infrared heaters to heat the water to the desired temperature. An infrared burner is a high efficiency gas burner which is fed an air/gas mixture of a specific concentration. The air/gas mixture flows onto a surface, otherwise known as the combustion surface, where it is ignited. The proportion of the air/gas mixture is preadjusted so that when the burner is ignited a burning zone is maintained at a set level above the combustion surface. Preferably, this burning zone is tuned by adjusting the gas/air flow rate and the back pressure such that burner performance and heat transfer are optimized. For example, U.S. Pat. No. 5,201,807 to Liljenberg et al. discloses the use of such an infrared burner in a water booster for a commercial warewasher. The Liljenberg invention includes a pump which continuously pumps water to be heated through a finned tube heat exchanger which is disposed in close proximity with the burner combustion surface.